Distributed processing systems in the telecommunications art are well known, and their number is rapidly proliferating. One type is shown in U.S. Pat. No. 4,127,742 issued Nov. 28, 1978 to G. Couturier, et al.
In that system, intercommunication between a group control and the system control is effected over a number of busses, a time division speech bus, various scanner control conductors, and other control conductors.
Also well known in the art are telecommunications systems for interconnecting multiple lines at multiple line telephone instruments over time-divided conductors, there being two speech conductors common to all lines having access to the instrument and two or more control conductors coupled to each instrument. Where the transmission of control data is bidirectional, only two control conductors are required, as shown by U.S. Pat. No. 3,935,396 issued to J. Barselotti, et al. on Jan. 27, 1976. Unidirectional transmission of data requiring four conductors--two for transmitting and two for receiving--is known by many U.S. patents, such as U.S. Pat. No. 3,475,256 issued July 1973 to R. L. Carbrey.